1. Field of the Invention
The present invention relates in general to the conversion of wind energy to electrical energy and, more particularly, to an orbital track wind turbine which provides a highly efficient method and apparatus for the conversion of wind energy to electrical energy.
2. Description of Related Art
It has become increasingly important due to environmental and economic considerations for the United States to transition from fossil fuels to renewable energy. Unless wind power is cost competitive, no amount of political action can make it successful in the long term. The primary and overriding issue in transition to wind power is the cost per kilowatt-hour of electrical power produced by wind in comparison to more conventional electric power generation systems.
Windmills have been used to pump water for literally thousands of years. In the United States, two and three-bladed, horizontal axis wind turbines are currently in use in California. A large number of such wind farms are currently located on certain mountain ranges and passes in California which have substantial wind velocities. High-speed, two-bladed, horizontal axis wind turbines can achieve power coefficients slightly greater than 45% at tip speed ratios approximating 6. Due to its high performance, this general approach, whether using two blades or three, has therefore been the primary focus of wind energy research and development.
A vertical type wind rotor design is disclosed in U.S. Pat. No. 1,766,765 to Savonius. The Savonius turbine is primarily a drag-type wind turbine. The rotor in Savonius comprises two oppositely curved vanes overlapping each other in the center, there being a gap between insides of the vanes. Savonius solved the problem of improperly designed turbines which create a partial vacuum behind the rotors. Savonius' solution was to allow a pathway for ram air from the downwind (power stroke side) to bleed over the upwind (power robbing side). However, it has been demonstrated that in the turbines of Savonius the tip speed of the turbines is never faster than the wind, resulting in lower efficiencies. State of the art wind turbines are lift devices with airfoils that move at a velocity that is faster than that of the wind.
Engineers have continued to design larger turbines, on ever taller towers. However, there may be limits to this approach. The Department of Energy recently indicated in a 2008 report that, “Many turbine designers do not expect the rotors of land-based turbines to become much larger than about 100 meters in diameter, with corresponding outputs of about 3 MW-5 MW”.
The nature of multiple turbine interference and incentives for larger swept areas at greater heights inspired the evolution of a cylinder shaped swept area, resembling that of a traditional H-rotor (VAWT) design shown in FIG. 1. One of the problems with the H-rotor is the long radial supports, which create drag and interfere with the turbine's efficiency. Therefore, engineers have realized that there is a major issue of wind interference in H-rotor designs involving the use of long radial arms to connect the blades to a central axis. As a result, it has been found that the H-rotor wind turbines are typically about one-third less efficient than wind turbines employing a horizontal rotor.
The metamorphosis of a pyramid design, first into a steeper sided shape, eventually led to the realization that a simple cylindrical geometry would provide the best blend of both aerodynamic and mechanical optimization. In addition, the wind industry desires to move from multiple turbines on one tower to a single large turbine. This approach eliminates interference associated with multiple towers, while still allowing for a large swept area.
It is therefore the principal object of the present invention to provide a wind turbine which can utilize large blades without the use of long radial arms connecting the blades to a central axis.
It is another object of the present invention to provide a wind turbine capable of achieving efficiency of wind conversion much higher than the efficiency achieved with conventional horizontal and vertical rotor wind turbines currently in use.
It is yet another object of the present invention to provide a wind turbine which can be scaled to much larger sizes and with greater efficiency than the conventional horizontal axis wind turbines currently in use.
It is still another object of the present invention to provide a new and improved wind turbine which is insensitive to wind direction, requires no long cantilevered rotor blades, and which uses low-cost and lightweight airfoils of constant cross-section. These airfoils are much lower cost to manufacture as compared to complex horizontal axis wind turbine airfoils.
It is another object of the present invention to provide a wind turbine that produces electric power at a lower cost per megawatt hour than the current wind turbine in use and which has a lower tower and footing cost than the current wind turbines in use, and in which the high maintenance items such as gear boxes and generators are located nearer the ground for convenience of maintenance.